1. Field of the Invention
The present invention relates to an organic electroluminescent device, and more particularly, to an active-matrix organic electroluminescent device for improving a device characteristic while protecting a channel layer of a thin film transistor.
2. Description of the Related Art
A self-luminous organic electroluminescent device, one of new flat panel display devices, has advantages of an excellent viewing angle characteristic and a high contrast ratio, compared to a liquid crystal display device. Also, the self-luminous organic electroluminescent device can be manufactured in lightweight, have a slim profile, and consume low power because a backlight is unnecessary. Advantageously, the organic electroluminescent device can be driven by a low DC voltage, has a fast response time, and is formed entirely of a solid. Therefore, the organic electroluminescent device is strongly resistant to an external impact, has a wide operating temperature range, and particularly, is cheap to manufacture.
FIG. 1 is a cross-sectional view illustrating a thin film transistor of a related art organic electroluminescent device.
As illustrated in FIG. 1, the thin film transistor used for an organic electroluminescent device includes a gate electrode 21 on a channel layer 14 of polysilicon, and a source electrode 16a and a drain electrode 16b on the channel layer 14 have a coplanar structure around the channel layer 14.
A buffer layer 11 is formed on an insulating substrate 10, and the channel layer 14 is formed on the buffer layer 11. The channel layer 14 is formed by forming amorphous silicon on the buffer layer 11, and polycrystallizing the amorphous silicon through a heat treatment using a laser.
Ohmic contact layers 15a and 15b are respectively formed at portions of the channel layer 14 contacting the source electrode 16a and the drain electrode 16b through n+ or p+ ion implantation.
A gate insulating layer 13 is formed on the channel layer 14. A storage electrode 23 for forming storage capacitance in cooperation with the gate electrode 21 is formed on the gate insulating layer 13.
The gate electrode 21 is formed on a portion of the channel layer 14 that is located between the ohmic contact layers 15a and 15b of the channel layer 14.
An interlayer insulating layer 17 is formed on the gate electrode 21. The source electrode 16a and the drain electrode 16b electrically contacting the ohmic contact layers 15a and 15b, respectively, are formed in the interlayer insulating layer 17. A pixel electrode 19 electrically contacts the drain electrode 16b. 
Thereafter, an organic electroluminescent body is formed on the pixel electrode 19. That is, the pixel electrode 19 serves as an anode or a cathode of the organic electroluminescent body in a pixel region.
However, the related art organic electroluminescent device has the following problems.
In the case of a bottom emission type organic electroluminescent device, the channel layer 14 is exposed to external light, which causes a device characteristic of the thin film transistor to change due to light energy.
This is because the external light is emitted directly onto the channel layer 14 from the outside of the insulating substrate 10, and holes or electrons included in the channel layer 14 receiving light energy have an influence on the characteristic of the thin film transistor.
To prevent the above problem, a light blocking pattern must be additionally formed to prevent exposure of the channel layer 14 to external light, which makes a fabrication process complicated.